1. Field of the Invention
The invention relates to an electrical system which includes a cable to transfer electrical power within the system. The invention further relates to the cable which transfers electrical power.
2. Background of the Related Art
It is well-known that in the distribution of electrical energy, electromagnetic emissions can occur. These emissions take the form of electric fields and magnetic fields.
Where the electrical energy being distributed is of relatively high voltage, relatively high current, or both, the electromagnetic emissions are often higher than in the distribution of low-level electrical signals. Where the distribution of electrical energy occurs in an automobile, there is further concern about electromagnetic emissions. One reason for this further concern is the large quantity of electronics in a typical automobile. Those electronics can be susceptible to electromagnetic emissions. Another reason for the concern is the relative proximity of the various electronic components in an automobile. A relatively small amount of electromagnetic emission can therefore affect a large number of electronic components.
It is known in the art to use coaxial cable to transfer low-level and higher power electrical signals. This coaxial cable has a center conductor surrounded by an insulator and an outer conductor. Current flowing in the cable flows in one conductor and returns in the other. The balancing of the currents substantially prevents electromagnetic emissions from the cable and substantially protects low-level signals in the cable from interference by external electromagnetic fields.
A useful form of electrical power is alternating-current multiple-phase power. There, each phase has a voltage which is separated from the other phase voltages by an angular difference. Ashley in U.S. Pat. No. 5,147,983 teaches one way to transfer multiple-phase electrical power. There, individual phases of a multiple-phase power distribution system are carried by coaxial cables. However, the result is a multiplicity of coaxial cables to carry the multiple phases. The multiplicity of coaxial cables can result in an undesirable bulk and weight. This bulk and weight are drawbacks especially in automobiles, where multiple-phase electrical power is becoming increasingly important as a power source for propulsion of electric automobiles.
Given the lack of attractive solutions to the problem of electromagnetic emissions due to the distribution of multiple-phase electrical power, a single cable which transmits multiple-phase power with little or no electromagnetic emissions would provide significant advantages over the prior art.